The overall goal of this clinical investigation will be to determine patterns of fatty acid metabolism in skeletal muscle of obese individuals and whether exercise training, alone or combined with weight loss, can enhance the capacity of muscle in obese individuals for lipid metabolism. Particular emphasis will be placed on determining mechanisms which cause lipid accumulation within skeletal muscle, an aspect of regional fat distribution which we posit is integrally linked to insulin resistance in obesity. The hypotheses to be tested is that fat accumulates within muscle of obese individuals due to an impaired capacity for lipid oxidation (in the face of essentially normal rates of fatty acid uptake) and that exercise but not weight loss can correct this impairment. The assessments proposed are nearly identical to those which have been used in previous studies of the effects of weight loss on fatty acid metabolism by muscle.